I was playing around with long exposures in the car the other day, when I realized something I never knew before, which is that my husband doesn't tend to stay in the same lane for more than a few seconds at a time. Every time I started an exposure, he would switch lanes on me. Fortunately, in this photo, he did it very smoothly and I ended up with what I think is a pretty cool result!
I really debated about how much to post-process this. In one version I darkened the sky to black and took out the light in the upper left, but it ended up looking too symmetrical. So I stuck with pretty much a straight conversion to black and white, and cropped to remove the front of the car and the dirty parts of the windshield.